Absorbent articles and methods of making

ABSTRACT

Described herein are absorbent articles and methods of making such articles. The articles are made by bonding a copolymer onto a substrate to form a core. The absorbent articles are particularly useful in personal care product, e.g., disposable hygiene products.

TECHNICAL FIELD

An absorbent article is described comprising bonded copolymer onto asubstrate to form a core and methods of making such articles, which areuseful in personal care products.

BACKGROUND

Personal care products for the absorption of body fluids are known. Suchproducts include adult incontinence products, diapers, training pants,feminine care products, wound dressings and the like. Traditionally,such personal care products generally comprise an amount of a cellulosicfiber such as wood pulp fluff. Wood pulp fluff is known to be a suitableabsorbent for body fluids. As a general rule, 1 gram of wood pulp fluffis able to absorb from about 5 to about 8 grams of a discharged bodyfluid such as urine. A personal care product such as an infant diaper,generally has an absorbent capacity of at least about 200 to 400 gramsof urine. Thus, when such an infant diaper is formed from wood pulpfluff, a relatively large quantity of wood pulp fluff must be employed.

In order to reduce the amount of wood pulp fluff and the correspondingbulk of such an infant diaper, it is known to include high absorbencymaterials known in the art as superabsorbents. Such high absorbencymaterials are generally capable of absorbing at least about 10,preferably at least about 20, and up to 50 or more times their weight inwater. By incorporating such high absorbency materials in infantdiapers, it is possible to reduce the overall bulk of the diaper whilemaintaining its absolute absorbent capacity.

Nonetheless, the use of such high absorbency materials is not withoutproblems. For example, some high absorbency materials are known to causegel blocking. That is, as the high absorbency materials become swollenwith a liquid, they form a gelatinous mass which prevents the free flowof liquid therethrough. Thus, while the high absorbency materials may beable to absorb an initial insult (in other words, exposure to fluid),subsequent insults are unable to pass through the now swollen highabsorbency material. As a result, subsequent insults tend to pool andrun off of the absorbent product resulting in leakage.

SUMMARY

There is a desire for absorbent articles, which have high absorbencycapacity and a rapid absorption rate. There is a desire to provide thinabsorbent articles with a high absorbent capacity. There is also adesire to be able to easily control or tailor the absorbency capacity ofabsorbent articles to the desired end use application withoutcompromising the rapid absorption rate. There is a need to providefacile processes that are amenable to roll-to-roll processing, and thusprovide ease of manufacturing.

In one aspect, an absorbent article is described comprising: (i) a firstsubstrate; and (ii) a copolymer irreversibly bonded onto the firstsubstrate to form a core, wherein the copolymer is derived from apolymerizable solution comprising: (i) a first monomer selected from a(meth)acrylic acid or salt thereof; (ii) greater than 1 wt % of a secondmonomer, wherein the second monomer is a hydrophilic crosslinkingmonomer; and (iii) a polymeric porogen, wherein at least 50% of theacidic functional groups in the core are neutralized with salt formingcations.

In another aspect, a method of making an absorbent article is describedcomprising: (a) contacting a polymerizable solution to a firstsubstrate, wherein the polymerizable solution comprises (i) a firstmonomer selected from a (meth)acrylic acid or salt thereof; (ii) greaterthan 1 wt % of a second monomer, wherein the second monomer is ahydrophilic crosslinking monomer; and (iii) a polymeric porogen; and (b)polymerizing the polymerizable solution to irreversibly bond a copolymeronto the first substrate forming a core, wherein at least 50% of theacidic functional groups in the core are neutralized with salt formingcations.

The above summary is not intended to describe each embodiment. Thedetails of one or more embodiments of the invention are also set forthin the description below. Other features, objects, and advantages willbe apparent from the description and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawing:

FIG. 1 is a schematic of an absorbent article, 10, of the presentdisclosure.

DETAILED DESCRIPTION

As used herein, the term

“a”, “an”, and “the” are used interchangeably and mean one or more;

“and/or” is used to indicate one or both stated cases may occur, forexample A and/or B includes, (A and B) and (A or B);

“copolymer” refers to a polymer comprising repeating units derived fromat least two different monomers and includes copolymers, terpolymers,etc.; and

“(meth)acrylate” refers to compounds containing either an acrylate(CH₂═CHCO⁻) or a methacrylate (CH₂═CCH₃CO⁻) structure or combinationsthereof.

Also herein, recitation of ranges by endpoints includes all numberssubsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75,9.98, etc.).

Also herein, recitation of “at least one” includes all numbers of oneand greater (e.g., at least 2, at least 4, at least 6, at least 8, atleast 10, at least 25, at least 50, at least 100, etc.).

The present disclosure is directed toward an absorbent core. Such corescan be used in personal care products. In the present disclosure, thecore comprises a substrate that has a copolymer bonded thereon.

Substrate

The substrate is not particularly limited so long as a copolymer isbonded thereon. The substrate may be a particle, fiber, film, or sheet.The substrate may be a woven or a nonwoven. The substrate may be from anatural fiber, such as cotton, or a synthetic fiber such as athermoplastic polymer.

Suitable particles include, but are not limited to, organic particles(such as carbon, activated carbon, styrene divinyl benene, crosslinked(meth)acrylates, organically modified inorganic particles, etc.), andinorganic particles (such as glass, ceramics, or metal oxides includingsilica, alumia, etc.). The particles may be porous or nonporousparticles. Typically the particles have an average diameter of at least0.1, 1, 5, 10, 20, or even 40 micrometers (μm) to at most 75 μm, 100 μm,500 μm, 1 millimeter (mm), 2 mm, 4 mm, 6.5 mm, or even 7 mm, althoughother size ranges may be contemplated based on the application. Theparticles could be used as an individual particle or the particles couldbe incorporated into another substrate for use, such as a nonwoven web.

The substrate may be a film or sheet. In one embodiment the thickness ofthe fiber, film or sheet is no more than 5 mm (millimeter), 2 mm, 1 mm,500 μm (micrometer), 100 μm, 20 μm, 2 μm, or even 1 μm.

In a preferred embodiment, the substrate is a nonwoven web which mayinclude nonwoven webs manufactured by any of the commonly knownprocesses for producing nonwoven webs. As used herein, the term“nonwoven web” refers to a fabric having a structure of individualfibers or fibers that are interlaid, but not in an identifiable manneras in a knitted or woven fabric.

Nonwoven webs can be made by wet laid, carded, air laid, spunlaced,spunbonding or melt-blowing techniques or combinations thereof.Spunbonded fibers are typically small diameter fibers that are formed byextruding molten thermoplastic polymer as filaments from a plurality offine, usually circular capillaries of a spinneret with the diameter ofthe extruded fibers being rapidly reduced. Meltblown fibers aretypically formed by extruding the molten thermoplastic material througha plurality of fine, usually circular, die capillaries as molten threadsor filaments into a high velocity, usually heated gas (e.g. air) streamwhich attenuates the filaments of molten thermoplastic material toreduce their diameter. Thereafter, the meltblown fibers are carried bythe high velocity gas stream and are deposited on a collecting surfaceto from a web of randomly dispersed meltblown fibers. Any of thenon-woven webs may be made from a single type of fiber or two or morefibers that differ in the type of thermoplastic polymer and/orthickness.

Further details on the manufacturing method of non-woven webs of thisdisclosure may be found in Wente, Superfine Thermoplastic Fibers, 48INDUS. ENG. CHEM. 1342(1956), or in Wente et al., Manufacture OfSuperfine Organic Fibers, (Naval Research Laboratories Report No. 4364,1954).

Suitable thermoplastic polymeric materials include, but are not limitedto, polyolefins, poly(isoprenes), poly(butadienes), fluorinatedpolymers, chlorinated polymers, polyamides, polyimides, polyethers,poly(ether sulfones), poly(sulfones), poly(vinyl acetates), polyesterssuch as poly(lactic acid), copolymers of vinyl acetate, such aspoly(ethylene)-co-poly(vinyl alcohol), poly(phosphazenes), poly(vinylesters), poly(vinyl ethers), poly(vinyl alcohols), and poly(carbonates).

Suitable polyolefins include, but are not limited to, poly(ethylene),poly(propylene), poly(l-butene), copolymers of ethylene and propylene,alpha olefin copolymers (such as copolymers of ethylene or propylenewith 1-butene, 1-hexene, 1-octene, and 1-decene),poly(ethylene-co-1-butene) and poly(ethylene-co-1-butene-co-1-hexene).

Suitable fluorinated polymers include, but are not limited to,poly(vinyl fluoride), poly(vinylidene fluoride), copolymers ofvinylidene fluoride (such as poly(vinylidenefluoride-co-hexafluoropropylene), and copolymers ofchlorotrifluoroethylene (such aspoly(ethylene-co-chlorotrifluoroethylene).

Suitable polyamides include, but are not limited to, typical nylonpolymers such as poly(iminoadipoyliminohexamethylene),poly(iminoadipoyliminodecamethylene), and polycaprolactam. Suitablepolyimides include, but are not limited to, poly(pyromellitimide).

Suitable poly(ether sulfones) include, but are not limited to,poly(diphenylether sulfone) and poly(diphenylsulfone-co-diphenyleneoxide sulfone).

Suitable copolymers of vinyl acetate include, but are not limited to,poly(ethylene-co-vinyl acetate) and such copolymers in which at leastsome of the acetate groups have been hydrolyzed to afford variouspoly(vinyl alcohols).

In some embodiments, the thermoplastic polymer substrate may be surfacetreated, such as by corona or plasma discharge, to provide suitablefunctionality to the surface of the substrate. Surface treatment canprovide functional groups such as hydroxyl groups that can improvewetting by the polymerizable solution or that can improve the degree ofgrafting of the copolymer. One such useful plasma treatment is describedin U.S. Pat. No. 7,125,603 (David et al.).

In one embodiment, the substrate is a porous substrate, for example amicroporous membrane such as a solvent-induced phase separation (SIPS)membrane or a thermally-induced phase separation (TIPS) membrane, whichare known in the art.

Copolymer

The substrate is surface modified with a copolymer, which is bonded uponthe substrate. The copolymer may be grafted to the substrate and/orcrosslinked onto the substrate, forming a polymer network that is noteasily removed from the substrate. The copolymer is derived from apolymerizable solution comprising a polymeric porogen and at least twodifferent monomers: (i) a (meth)acrylic acid monomer or salt thereof;and (ii) a cross-linking hydrophilic monomer.

The (meth)acrylic acid monomer includes acrylic acid and salts thereofand/or methacrylic acid and salts thereof. Suitable salts of(meth)acrylic acid include those known in the art, including alkalimetal salts, ammonium salts, amine salts, etc.

The a second monomer is a hydrophilic crosslinking monomer.

Suitable crosslinking monomers are those compounds having two or moreethylenically unsaturated groups capable of copolymerizing with thefirst and the second monomers.

Exemplary hydrophilic crosslinking monomers include: N,N′-methylenebisacrylamide, N,N′-methylene bismethacrylamide, bis(2-methacryloxyethyl) phosphate, 1,4-butanediol diacrylate,1,4-butanediol dimethacrylate, diethylene glycol diacrylate, diethyleneglycol dimethacrylate, glycerol trimethacrylate, triallyl cyanurate,triethylene glycol diacrylate, or others such as known in the art inorder to produce a cross-linked and/or branched graft polymer and thelike. Preferred second monomers include those selected from at least oneof methylenebisacrylamide, polyethyleneglycoldiacrylate, andcombinations thereof.

Previously, it has been thought that the amount of crosslinker used inabsorbent articles needed to be kept low to provide sufficientabsorbance capacity. See for example Omidian, H., et al. in Journal ofApplied Polymer Science, vol. 54, (1994), p. 241-249, with is directedtoward acrylic-based superabsorbents and teaches that the absorption isdependent on the amount of crosslinker used, indicating that the amountof crosslinker needs to be kept low. Also see U.S. Pat. No. 6,417,425(Whitmore et al.) which discloses an absorbent article made via agrafting process using less than about 1 mole percent of crosslinker.

Surprisingly, in the present disclosure, it has been found that using atleast 1 wt % of the crosslinking monomer versus the total monomer weightresults in good absorption properties. The amount of the hydrophiliccrosslinking monomer employed in the present disclosure will depend onthe nature of this monomer and the polymerization method used. If toolittle crosslinking occurs, the copolymer can be rinsed from the surfaceof the substrate. This is particularly relevant when using a Type Iphotoinitiator, as opposed to a Type II photoinitiator, since covalentgrafting of the polymerizable solution to the surface does not occur. Iftoo much crosslinking occurs, absorbency capacity decreases, or the rateof absorption decreases, or both. In one embodiment, at least 1%, 2%,3%, 4%, or even 5% by weight and no more than 30%, 25%, 20%, 15%, oreven 10% by weight of the second monomer versus the total weight ofmonomer can be used.

The copolymer described here is a polymer comprising repeating unitsderived from the recited monomers described above. In one embodiment,the polymerizable solution comprises additional monomers to yield acopolymer with specific properties. The additional monomers may or maynot be crosslinking and may or may not be hydrophilic. For example,additional monomers may be used, such as a hydrophilic non-crosslinkingmonomer, including monoethylenically unsaturated compounds (or compoundshaving a polymerizable double bond) having at least one hydrophilicradical, such as carboxyl, carboxylic acid anhydride, carboxylic acidsalt, sulfonic acid, sulfonic acid salt, hydroxyl, ether, amide, aminoand quaternary ammonium salt groups. In one embodiment, thepolymerizable solution comprises a third monomer selected from at leastone of 2-hydroxyethylmethacrylate, 2-hydroxypropyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, N,N-dimethylacrylamide, and acrylamide,and combinations thereof. See co-filed application XXXX (3M DocketNumber 75040US002, filed contemporaneously with the presentapplication), herein incorporated by reference in its entirety.

In the present disclosure, a polymeric porogen is added to thepolymerizable solution to create permanent pores in the polymerizedcopolymer. Added porogens typically influence the timing of phaseseparation of the forming polymer network from the rest of the monomerphase mixture. The size of the pore formation may be dependent not onlyon the polymeric porogen selected, but also the interaction between thecomonomers and the selected porogen(s), the mass ratio between thenon-cross-linking monomer and the cross-linking monomer, the chemicalstructure of the non-cross-linking monomer, the amount of porogen, thetype of optional cosolvent, the amount of optional cosolvent, orcombinations thereof.

In the present disclosure, the polymeric porogen is a polymer having amolecular weight of at least 200, 500, 1000, 2000, 4000 or even 6000g/mol. Examples of polymeric porogens include: polyethylene glycol,polypropylene glycol, and combinations thereof. Commercially availablepolymeric porogens include: PEG 3350, PEG 6000, and PEG 8000.

In one embodiment, the polymerizable composition comprises at least 1%,2%, 3%, 4%, or even 5 wt % polymeric porogen and no more than 30%, 25%,or even 20% by wt polymeric porogen based on the total weight of themonomers.

Method of Making

The copolymer of the present disclosure is irreversibly bonded upon thesubstrate. As used herein irreversibly bonded means that the copolymeris either covalently bonded (or grafted) to the substrate and/or isphysically crosslinked onto the substrate such that, when the compositecontaining the polymerized copolymer is soaked in deionized water for atleast 30 minutes, the copolymer remains firmly attached to thesubstrate. That is, the copolymer does not dissolve or wash away, andthe physical presence of the swollen copolymer on the surface of thesubstrate is obvious by visual or tactile observation. In the presentdisclosure, a polymerizable solution is prepared comprising themonomers, a solvent, and, optionally, a photoinitiator.

In the method of the present disclosure, the photoinitiator may be TypeI or Type II.

When using Type I initiators, the copolymer is physically crosslinkedonto the substrate. Type I initiators work via an alpha-cleavage whichforms two radical species. At least one of the radical species initiatespolymerization of the monomer(s). Incorporation of the crosslinkingmonomer(s) results in a crosslinked coating on the surface of thesubstrate. Exemplary Type I initiators include benzoin ethers such asbenzoin methyl ether and benzoin isopropyl ether; substitutedacetophenones such as 2, 2-dimethoxyacetophenone, available under thetrade designation “IRGACURE™ 651” photoinitiator (Ciba SpecialtyChemicals), 2,2 dimethoxy-2-phenyl-1-phenylethanone, available under thetrade designation “ESACURE KB-1” photoinitiator (Sartomer Co.; WestChester, Pa.),1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one,available under the trade designation “IRGACURE 2959” (Ciba SpecialtyChemicals), and dimethoxyhydroxyacetophenone; substituted α-ketols suchas 2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such as2-naphthalene-sulfonyl chloride; and photoactive oximes such as1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularlypreferred among these are the substituted acetophenones, and especially1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one due toits water solubility.

Type II initiators work to facilitate hydrogen abstraction from thesurface of the substrate to provide an incipient free radical, and freeradical addition of the monomer(s) to produce the grafted copolymer.When using Type II initiators, the copolymer is typically grafted ontothe substrate, however the copolymer may be physically crosslinked ontothe substrate as well. In order for the grafting of the copolymer tooccur, the substrate must comprise an abstractable atom (e.g., ahydrogen or halogen). Type II initiators used in the present disclosureinclude those of the general formula:

Ar—CO—R¹³

in which Ar is a substituted or unsubstituted aryl group having 6 to 12carbon atoms optionally substituted with a C₁ to C₁₂ alkyl group, a C₁to C₁₂ alkoxy group, or a phenyl group; and R¹³ is a C₁ to C₆ alkylgroup, a cycloalkyl group having 3 to 14 carbon atoms, or Ar. ExemplaryType II initiators include benzophenone,4-(3-sulfopropyloxy)benzophenone sodium salt, Michler's ketone, benzil,anthraquinone, 5,12-naphthacenequinone, aceanthracenequinone,benz(A)anthracene-7,12-dione, 1,4-chrysenequinone,6,13-pentacenequinone, 5,7,12,14-pentacenetetrone, 9-fluorenone,anthrone, xanthone, thioxanthone, 2-(3-sulfopropyloxy)thioxanthen-9-one,acridone, dibenzosuberone, acetophenone, and chromone.

An effective amount of Type I or Type II initiator is used to triggerpolymerization of the monomer and enable grafting or coating of thecopolymer onto the substrate. The photoinitiators can be used in amountsfrom about 0.001 part by weight to about 15 parts, preferably from about0.5 to about 5 parts, by weight based on 100 parts total monomer.

A solvent can be used in the polymerizable solution to solublize themonomers and the optional photoinitiator. The solvent may be any polarsolvent. In many embodiments the solvent is water or awater/water-miscible organic solvent mixture. The ratio of water toorganic solvent can vary widely, but is typically greater than about 1:2(v/v) water to organic solvent. Water is an important component of thesolvent mixture for solubility purposes, especially when a portion ofthe first monomer component is in its neutralized form. The organicsolvent may be an important component of the solvent mixture for thepurpose of improving the wetting of the substrate, especially when thesubstrate is hydrophobic. The organic solvent can also promotesolubility of the photoinitiator in the mixture.

Any such water miscible organic solvent preferably has no groups thatwould retard the polymerization. In some embodiments, the water misciblesolvents are protic containing organic liquids such as the loweralcohols having 1 to 4 carbon atoms, lower glycols having 2 to 6 carbonatoms, and lower glycol ethers having 3 to 6 carbon atoms and 1 to 2ether linkages. Specific examples are methanol, ethanol, isopropanol,n-butanol, t-butyl alcohol, ethylene glycol, methoxyethanol,ethoxyethanol, propoxyethanol, butoxyethanol, methyl carbitol, ethylcarbitol, and mixtures thereof.

In other embodiments, non-protic water miscible organic solvents canalso be used such as ketones, amides, and sulfoxides such as acetone,methyl ethyl ketone, methyl propyl ketone, dimethylformamide,dimethylacetamide, and dimethyl sulfoxide.

The concentration of each component in the polymerizable solution mayvary depending on a number of factors including, but not limited to, theidentity of the monomers in the polymerizable solution, the identity ofthe initiator, the extent of grafting or crosslinking desired, thereactivity of the monomer(s), and the solvent used.

Typically, the total solids range in the polymerizable solution is fromabout 0.1 wt % to about 60 wt %, desirably, from about 1 wt % to about35 wt %, more desirably, from about 5% to about 25%, based on a totalweight of the polymerizable solution.

In the present disclosure, the substrate is contacted with thepolymerizable solution (comprising at least the monomers, the porogen,the solvent, and the optional photoinitiator) to form a treatedsubstrate. The substrate may be imbibed or coated with the polymerizablesolution using conventional techniques known in the art, including butnot limited to, dip coating, roll coating, spray coating, knife coating,gravure coating, extrusion, die-coating, and the like.

After the substrate has been treated with the polymerizable solution itis often desirable to remove the excess treatment fluid by squeezingand/or blotting, and this is particularly desirable when it is desiredto form a thin coating of bonded polymer on the surface of a nonwovenweb or film or foam material. This may be done by the simple expedientof passing the treated substrate through a nip formed between rollers,such as rubber or rubber coated rollers, to squeeze off the excesstreatment fluid, and/or vacuum suction, and/or by blotting the treatedsubstrate with absorbent media such as paper or cloth towels or thelike.

However, it may also be highly desirable for certain applications thatone or both surfaces of a substrate such as a polymeric film material becovalently bonded or coated with a thicker coating of the copolymer suchthat the bonded copolymer may serve as a coating of hydrogel. Suchhydrogel coated films are useful for many medical applicationsincluding, but not limited, to such as defibrillator pads, cardiacmonitoring electrode pads, transdermal drug delivery patches, and thelike. Where a thicker coating of the bonded copolymer is desired it maybe desirable to avoid removing excess treatment fluid.

The treated substrate, coated with the polymerizable solution, then issubjected to an activation energy to polymerize or graft the monomersonto the substrate. The activation energy generates free radicals insolution (by cleaving at least some of the Type I photoinitiatormolecules to form free radicals) or on the surface of the substrate (byexciting the Type II photoinitiator molecules which then abstract anatom from the substrate). Electron beam or gamma irradiation can also beused to provide the activation energy necessary to generate freeradicals in solution or on the surface of the substrate (the addition ofa photoinitiator is not necessary in these cases). The free radicalsthen initiate polymerization of the monomer either in solution orstarting at the surface radical sites which were formed by exposure tothe activation energy.

The activation energy may be provided by methods as are known in theart, such as for example by exposure to ultraviolet radiation, electronbeam radiation, or gamma radiation. The conditions under which theirradiation is conducted, such as radiation intensity and time maydiffer depending on the type of substrate used, the amount of monomerapplied to the substrate, the type of irradiation, and the like.

Radiation may be applied using a conventional ultraviolet radiation (UV)such as may be provided by excimer lamp or other UV emitting lamp.Irradiation is generally conducted using a UV lamp with an intensity inthe range of from 100 to 700 watts per inch (“W/in”), preferably in therange of from 400 to 600 W/in for 0.1 seconds to 15 minutes or more,with the distance between the UV lamp and the substrate being 2 to 30centimeters.

Electron beam polymerization or grafting can be accomplished using acommercially available electron beam accelerator, such as thoseavailable under the trade designation ELECTOCURTAIN CB 175 (EnergySciences, Inc., Wilmington, Ma.). Accelerators operating in the 150 to300 kilovolt range are acceptable. The beam current on such systems,typically 1 to 10 milliamperes, can be adjusted to obtain the desireddose of ionizing radiation. In general, it is desirable to irradiate thecoated substrate with doses from about 1 to 16 megarads, more preferably2 to 8 megarads. Particularly when using lower doses, it is desirable topurge oxygen from the polymerizable solution (as by bubbling nitrogenthrough the solution). The maximum dose would be that dose at whichdegradation of the substrate begins.

Desirably, the coated substrate will be subjected to the activationenergy in a reduced oxygen or non-oxidative environment, such as byplacing the coated substrate in a reaction vessel or passing thepolymeric substrate through a reaction chamber from which the air hasbeen purged prior to energy activation of the monomer. The air may bepurged from such a reaction vessel or chamber by purging with inert gassuch as argon or nitrogen. This is desirable because atmospheric oxygencan act as a reaction terminator by combining with the surface radicalsites formed from the radical forming groups on the surface of thesubstrate, and thereby reduce the number of initialization sitesavailable to the monomer. In many instances it is sufficient to sandwichthe coated substrate between two sheets of a thermoplastic polymericfilm, such as polyester or polyolefin film.

The temperature during irradiation is not critical and may be done atroom temperature.

Although thermal processes are not preferred for reasons of solventvolatility, thermal polymerization or curing of the treated substrate ispossible. For thermal curing there are no particular limitations on thetype of reaction vessel used. For batch polymerizations, sprayed websmay be cured in an oven in an air or inert atmosphere, and optionallyunder vacuum. In the case of a continuous process, the web may be passedthrough a dryer, such as an infrared (“IR”), through air or the like.The polymerization temperature can vary depending on the thickness ofthe substrate, the concentration of monomer, the type of solvent used,and the type and amount of thermal initiator used in the blend. Thepolymerization is typically in the range of from 0° C. to 150° C. andpreferably in the range of from 10° C. to 100° C., and more preferablyin the range of 20° C. to 50° C. The polymerization time depends on thepolymerization temperature and the identity of the initiator, but istypically several seconds to 2 hours and preferably several seconds to10 minutes. Preferred initiators for thermal processes are redoxinitiators, many of which are well known in the art.

After irradiation, the coated substrate may optionally be washed toremove unpolymerized monomer(s), noncrosslinked polymer, and/ornongrafted polymer, if desired.

After irradiation and optional washing, the substrate with thecovalently bonded copolymer thereon may be dried to remove the solventby such means as forced air ovens, infrared lamps and the like.

Although not wanting to be limited by theory, it is believe that thepolymeric porogens during polymerization create pores within thepolymerized structure. It is believed that the pores are formed, atleast in part, by the exclusion of the aqueous solvent from thepolymerizing material as its molecular weight increases. When themolecular weight of the growing polymer becomes sufficiently large, apolymeric phase separates from the aqueous phase. The point at whichphase separation occurs can influence the average pore size and the poresize distribution.

The point at which phase separation occurs can be influenced by thecompatibility of the polymeric porogen with the forming polymericmaterial and the amount of porogen. Additionally, the point at whichphase separation occurs can be influenced by the amount of crosslinkingmonomer present in the polymerizable solution, with larger amounts ofcrosslinking monomer typically favoring earlier phase separation due toa more rapid increase in the molecular weight of the polymeric material.

Polymeric porogens that are compatible with the forming polymericmaterial (i.e., porogens that are good solvents for the formingpolymeric material) tend to result in a later phase separation comparedto porogens that are less compatible with the forming polymeric material(porogens that are poor solvents for the forming polymeric material).

Because the polymer network is believed to form around the polymericporogens, in one embodiment, washing of the substrate with the copolymerbonded thereon, can be used to wash away the polymeric porogens,evacuating the pores within the core. Ideally, the washing solutioncomprises a solvent which is polymeric porogen is soluble in, such aswater, alcohol, or another organic solvent. In one embodiment drying maybe used to evacuate the pores of the core of the polymeric porogenand/or solvent.

The substrate with the copolymer bonded thereon can be processed eitherin a batch to batch process or a continuous process. In a preferredembodiment, the substrate comprises a sufficient length, such that thesubstrate (e.g., a web) is processed in a continuous fashion, throughfor example, coating with the polymerizable solution, irradiation, andoptional washing and drying; making a roll good and enabling the highthroughput manufacture of an absorbent core.

Depending on the desired end use for the substrate with the copolymerbonded thereon, it may be desirable to convert the acidic monomer orpolymer to its conjugate base form before, during, or after processing.While both the acid form of the polymer and the conjugate base form ofthe polymer are hydrophilic and allow the coated polymeric substratematerial to be wetted with aqueous liquids, the conjugate base form ispreferred for end uses where high liquid absorbency is desired. Thepolymer may be converted to its conjugate base form by methods known inthe art such as a neutralization reaction with up to a molar equivalentof a strong base such as sodium hydroxide or potassium hydroxide toyield the conjugate base/conjugate acid salt. For example, sodiumacrylate or potassium acrylate would result from the neutralization ofan acrylic acid monomer using the two bases disclosed above. Wheredesired, partial neutralization might be accomplished by titrating theacid groups with the base such that less that 100 percent conversion tothe salt form is achieved.

The resulting core, comprising the substrate with the copolymer bondedthereon, is neutralized such that no more than 100% and at least 50, 60,70, 80, 90, or even 95% of the acidic functional groups in the core areneutralized with salt forming cations.

The core, in an absorbent product, is a layer used to contain the bulkof the liquid assault. Therefore, the core should have a rapid uptake ofthe liquid and minimal gel blocking. Ideally, it is preferable if thecore can absorb at least 10 times, 20 times, 40 times or even 50 timesits weight in deionized water and at least 5 times, 10 times, 15 times,or even 20 times its weight in urine. Depending on the application, inone embodiment, it may be preferable that the core absorb liquid in aquick fashion, for example absorbing liquid (such as deionized water orsaline) in less than 90 sec, 60 sec, 40 sec, 20 sec, or even 10 sec whentested using the Test method of liquid absorption rate given in theExample section.

The absorbent structures or cores, described above are suitable for usein disposable absorbent products such as diapers, training pants, adultincontinence products, feminine care products, animal care products,wound dressings, chemical absorbent pads and the like. Methods offorming such absorbent products and the absorbent products formedthereby are known to those skilled in the art.

The core described above, may be used alone or may be combined with oneor more layers to form an absorbent article as shown in FIG. 1. Core 12comprises a first substrate with a copolymer covalently bonded thereon.Core 12 may be contacted with second substrate 14, which is a liquidpervious layer. Optionally, or in addition to second substrate 14, core12 may be contacted with third substrate 16, which is a liquidimpervious layer. If both second substrate 14 and third substrate 16 arepresent, core 12 is sandwiched therebetween. The second substrate 14 andthird substrate 16 may be directly contacting core 12, or there may beoptional layers therebetween to facilitate construction or performance,for example adhesive layers between the substrates or an additionallayer(s) to provide enhanced properties such as performance. However,second substrate 14 is in liquid communication with core 12. Optionally,third substrate 16 is in liquid communication with core 12.

Typically an absorbent product comprises a liquid pervious layer, orsecond substrate, between the body of the subject and the core. Thisliquid pervious layer should exhibit rapid uptake of fluid, goodtransfer properties, good uptake upon repeated insults with fluid, andgood skin compatibility, among other things. Such liquid pervious layersare known in the art and can include, for example, porous polyesters,porous polyolefins, porous rayon, cotton, and combinations thereof.

Typically an absorbent product comprises a liquid impervious layer, orthird substrate, which contains the liquid within the absorbent product,preventing leakage or seepage of the fluid. Such liquid imperviouslayers are known in the art and can include, for example, a nonporouspolyolefin.

The following is a list of exemplary embodiments of the presentdisclosure:

Embodiment 1

An absorbent article comprising:

a first substrate; and

a copolymer irreversibly bonded onto the first substrate to form a core,wherein the copolymer is derived from a polymerizable solutioncomprising:

-   -   (a) a first monomer selected from a (meth)acrylic acid or salt        thereof;    -   (b) greater than 1 wt % of a second monomer, wherein the second        monomer is a hydrophilic crosslinking monomer, and    -   (c) a polymeric porogen    -   wherein at least 50% of the acidic functional groups in the core        are neutralized with salt forming cations.

Embodiment 2

The absorbent article of embodiment 1, wherein the polymeric porogen hasa molecular weight of at least 200.

Embodiment 3

The absorbent article of any one of the previous embodiments, comprising1 wt % of the polymeric porogen.

Embodiment 4

The absorbent article of any one of the previous embodiments, comprisingthe polymeric porogen is selected from polyethyleneglycol andpolypropyleneglycol and copolymers thereof.

Embodiment 5

The absorbent article of any one of the previous embodiments, whereinthe polymerizable solution further comprises a third monomer, whereinthe third monomer is selected from at least one of2-hydroxyethylmethacrylate, 2-hydroxypropyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, N,N-dimethylacrylamide, and acrylamide.

Embodiment 6

The absorbent article of any one of the previous embodiments, whereinthe second monomer is selected from at least one ofmethylenebisacrylamide and polyethyleneglycoldiacrylate.

Embodiment 7

The absorbent article of any one of the previous embodiments, furthercomprising a second layer, wherein the second layer is a liquid perviouslayer.

Embodiment 8

The absorbent article of embodiment 7, wherein the second layer isselected from polyester, polyolefin, rayon, cotton, and combinationsthereof.

Embodiment 9

The absorbent article of any one of embodiments 7 or 8 furthercomprising a third layer, wherein the third layer is a liquid imperviouslayer and the core sandwiched between the second layer and the thirdlayer.

Embodiment 10

The absorbent article of embodiment 9, wherein the third layer isselected from a polyolefin.

Embodiment 11

The absorbent article of any one of the previous embodiments, whereinthe first substrate is selected from at least one of a thermoplastic anda fabric.

Embodiment 12

The absorbent article of any one of the previous embodiments, whereinthe first substrate is selected from at least one of a polypropylene,polyethylene, polyamide, cotton, and cellulose.

Embodiment 13

The absorbent article of any one of the previous embodiments, whereinthe absorbent article is selected from a diaper, a feminine hygiene pad,an animal hygiene pad, a wound care article, and a chemical absorbentpad.

Embodiment 14

A method of making an absorbance article comprising:

-   -   (a) contacting a polymerizable solution to a first substrate,        wherein the polymerizable solution comprises (i) a first monomer        selected from a (meth)acrylic acid or salt thereof; (ii) a        polymeric porogen; and (iii) greater than 1 wt % of a second        monomer, wherein the second monomer is a hydrophilic        crosslinking monomer; and    -   (b) polymerizing the polymerizable solution to irreversibly bond        a copolymer onto the first substrate forming a core,    -   wherein at least 50% of the acidic functional groups in the core        are neutralized with salt forming cations.

Embodiment 15

The method of embodiment 14, wherein the polymerizable solution furthercomprises a photoinitiator.

Embodiment 16

The method of embodiment 15, wherein the photoinitiator is a Type IIphotoinitiator.

Embodiment 17

The method of any one of embodiments 14-16, wherein the polymerizablesolution is contacted to the first substrate by a coating process.

Embodiment 18

The method of embodiment 17, wherein the coating process comprises atleast one of: knife coating, gravure coating, and dip coating.

Embodiment 19

The method of any one of embodiments 14-18, wherein the polymerizationis initiated with UV or e-beam radiation.

Embodiment 20

The method of any one of embodiments 14-19, further comprising washingthe core.

Embodiment 21

The method of any one of embodiments 14-20, further comprising dryingthe core.

Embodiment 22

The method of any one of embodiments 14-21, where the absorbent articleis a roll good.

EXAMPLES

Advantages and embodiments of this disclosure are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. In theseexamples, all percentages, proportions and ratios are by weight unlessotherwise indicated.

All materials are commercially available, for example from Sigma-AldrichChemical Company; Milwaukee, Wis., or known to those skilled in the artunless otherwise stated or apparent.

These abbreviations are used in the following examples: g=gram,gsm=grams of polymer per square meter, kg=kilograms, sec=seconds,min=minutes, mol=mole; cm=centimeter, mm=millimeter, mL=milliliter,L=liter, v=volume, and wt=weight.

Test Methods

Test Method for Liquid Absorption Amount

Three 24 mm diameter disks were die-cut from each sample, individuallyweighed, then placed into 5 mL polypropylene centrifuge tubes containing4.5 mL of liquid (deionized water or 0.9% wt/wt saline (sodium chloridesolution)). The centrifuge tubes were capped and gently rotated for 15min. The swollen disks were removed with forceps, allowed to drip for 60sec to remove excess liquid, and then reweighed. The absorption amount,A_(x), expressed in grams of liquid absorbed per gram of compositesubstrate (g/g), was calculated according to the following equation:

A_(x)=(W_(w)−W_(d))/W_(d)

where W_(w) is the wet weight of the disk and W_(d) is the dry weight ofthe disk. Results are recorded as the average of the three measurements.

Test Method for Liquid Absorption Rate

A qualitative test was devised to compare the absorption rates ofvarious samples. Two drops of liquid (deionized water or 0.9% wt/wtsaline) were deposited from a polypropylene disposable pipet onto thesubstrate. The length of time needed for the liquid to be completelyabsorbed into the material was observed, and recorded as the absorptiontime (A) in sec. Each sample was tested in triplicate and the averagewas reported.

Preparation of S-BP: 4-(3-sulfopropyloxy)benzophenone, sodium salt

Sodium hydride (6 grams of a 60% by weight dispersion in mineral oil)was weighed into a 500 mL round bottom flask. Petroleum ether (15 mL)was added and swirled to dissolve the mineral oil. The liquid wasdecanted. Washing was repeated two more times with petroleum ether,decanting each time. Tetrahydrofuran (200 mL) was then added to theflask. Solid 4-hydroxybenzophenone (19.8 grams) was added portion-wiseover a period of about 10 min to control the rate of gas evolution. Theresultant yellow mixture was stirred for 30 min, propane sultone (13.4grams, Alfa Aesar, Ward Hill, Mass.) was added, stirred for 30 min, thenrefluxed overnight. The mixture was cooled to room temperature,isopropanol (15 mL) was added, stirred 30 min, and the solid wasfiltered, and dried under a stream of nitrogen to provide the desiredproduct (33.8 grams) as an off-white solid. A 0.1 gram/mL solution indeionized water was prepared for use with the example preparationsbelow.

Preparation of Monomer Stock Solution

A monomer solution (20% wt/wt acrylic acid, 75% neutralized with sodiumhydroxide) was prepared from acrylic acid (12.27 grams), 5 N sodiumhydroxide solution (25.56 mL), diluted to a total of 60 grams with a 1:1v/v mixture of ethanol and deionized water.

Comparative Example C1

20% solids solution: A polymerizable solution was prepared by mixingabout 5.0 g of Monomer Stock Solution with 250 μL of S-BP. Variousamounts of methylenebisacrylamide (MBA) was added to the polymerizablesolution to provide varying amounts of crosslinker based on totalmonomer weight.

15% solids solution: A polymerizable solution was prepared by dilutingabout 3.6 g of Monomer Stock Solution with 1:1 v/v mixture of ethanoland deionized water to achieve about 5.0 g and adding 250 μL of S-BP.Various amounts of methylenebisacrylamide (MBA) was added to thepolymerizable solution to provide varying amounts of crosslinker basedon total monomer weight.

10% solids solution: A polymerizable solution was prepared by dilutingabout 2.5 g of Monomer Stock Solution with 1:1 v/v mixture of ethanoland deionized water to achieve about 5.0 g and adding 250 μL of S-BP.Various amounts of MBA was added to the polymerizable solution toprovide varying amounts of crosslinker based on total monomer weight.

5% solids solution: A polymerizable solution was prepared by dilutingabout 1.2 g of Monomer Stock Solution with 1:1 v/v mixture of ethanoland deionized water to achieve about 5.0 g and adding 250 μL of S-BP.Various amounts of MBA was added to the polymerizable solution toprovide varying amounts of crosslinker based on total monomer weight.

For each example, a 9 cm×12 cm piece of polyamide membrane (singlereinforced layer NYLON 6.6, three zone membrane, nominal pore size1.3-1.6 μm, product number BK080 (previously available from 3MPurification, Inc., Meridan Conn.)) was placed on a piece of polyester(PET) film and approximately 4.5 mL of polymerizable solution waspipetted onto the top surface of the membrane. The solution was allowedto soak into the membrane for about 1 minute. A second polyester filmwas placed on top of the substrate to form a “sandwich” construction ofPET/coated polyamide/PET. A 2.28 kg weight was rolled over the top ofthe sandwich construction and the excess coating solution that wassqueezed out was removed. The construction was then irradiated using aUV stand (Classic Manufacturing, Inc., Oakdale, Minn.) equipped with 18bulbs (Sylvania RG2 40W F40/350BL/ECO, 10 above and 8 below thesubstrate, 46 inches long, spaced 2 inches on center) with anirradiation time of 10 min. The polyester films were removed, and thegrafted polyamide substrate was placed in a 250 mL polyethylene bottle.The bottle was filled with 0.9 wt % saline, sealed, and shaken for 30minutes to wash off residual monomer or ungrafted polymer. The salinewas poured off, replaced with fresh saline solution, and washed for 30min. The grafted substrate was finally washed for 30 min with deionizedwater and allowed to dry. The resulting substrates were tested fordeionized water absorption following the Test method for liquidabsorption amount described above. The results are shown in Table 1.

TABLE 1 Monomer Monomer Monomer Monomer 5% Solids 10% Solids 15% Solids20% Solids % MBA Water A_(x) (g/g) 1.0 4.1 2.5 2.4 2.8 0.5 2.0 3.3 11.612.4 0.25 NT 3.8 3.0 13.3 NT = not tested

Comparative Example C2

The procedure from Comparative Example C1 was similarly followed exceptthat the polyamide was replaced two different polypropylene nonwovens:

(1) White PP: a white spunbond material of 12-15 gsm, and

(2) Blue PP: a blue thermobonded material of 18 gsm basis weight(available from Shalag Industries, Ltd., Oxford, N.C., product numberSH-PPL-18B).

The polypropylene sheet was used individually or layered (2 sheets or 3sheets). The polymerizable solution as described in Comparative ExampleC1 comprising 20% solids and 0.5% MBA was used. Deionized water and 0.9%wt/wt saline solution absorption was measured following the Test methodfor liquid absorption amount and Test method for liquid absorption ratedescribed above. The results for liquid absorption amount are shown inTable 3. The liquid absorption rate for the various samples showedabsorption times of about 90 to >120 sec, possibly due to the“gel-block” phenomenon.

TABLE 2 White PP Blue PP Number water Saline water Saline of layersA_(x) (g/g) A_(x) (g/g) A_(x) (g/g) A_(x) (g/g) 1 97.4 19.4 111.5 23.0 268.2 14.3 70.1 16.4 3 50.0 13.6 44.6 15.4

Example 1

A polymerizable solution was prepared by adding polyethyleneglycol 2000(PEG 2000, 15% by weight) to a neutralized acrylic acid solutionprepared as in Comparative Example C1. Polymerizable solutions (5 geach) were prepared as described in Comparative Example C1 by addingS-BP and varying the amounts of MBA to provide varying amounts ofcrosslinker based on total monomer weight. These polymerizable solutionswere coated and grafted onto the Blue PP (2 layers). The coating processwas modified slightly from that described in Comparative Example C1 inthat the 2.28 kg weight was not used to remove excess polymerizablesolution. Instead, the top PET film, which was adhesively connected tothe bottom PET film was gently laid on top of the coated substrate andthe weight of the top PET was substantial enough to squeeze out excesspolymerizable solution. The grafted materials were then washed, dried,and evaluated for water and saline absorption (both absorption rate andamount). Washing was accomplished by soaking the grafted composites inthe appropriate wash liquid (0.9% saline or deionized water, 500 mL ofliquid per substrate piece) for 30 min with occasional gentle agitation.The same sequence of three washes as before was used. Saline anddeionized water absorption was measured following the Test method forliquid absorption amount and Test method for liquid absorption ratedescribed above. Testing results for Example 1 are listed in Table 3.

TABLE 3 Water 0.9% Saline MBA (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 0.5 >120 17.4 47 8.8 1 20 8.7 25 2.4 2 46 37.3 24 11.1 5 2426.2 10 8.4 7.5 9 10.7 6 4.2 10 8 10.2 8 6.4 15 3 9.1 2 3.4 20 2 5.8 24.4

Example 2

Example 2 was prepared and evaluated in the same fashion as Example 1except that the PEG 2000 was replaced with PEG 3350 (polyethyleneglycol3350). The results are shown in Table 4.

TABLE 4 Deionized Water 0.9% Saline MBA (%) A_(t) (sec) A_(x) (g/g)A_(t) (sec) A_(x) (g/g) 0.5 >120 4.1 >120 2.2 1 >120 21.0 >120 9.42 >120 33.5 >120 11.3 5 38 23.1 19 11.4 7.5 5 17.0 5 8.2 10 12 8.5 136.3 15 14 5.2 10 4.6 20 3 4.2 3 3.7

Example 3

Example 3 was prepared and evaluated in the same fashion as Example 1except that the PEG 2000 was replaced with PEG 6000 (polyethyleneglycol6000). The results are shown in Table 5.

TABLE 5 Water 0.9% Saline MBA (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 0.5 >120 0.2 >120 0.1 1 >120 0.9 >120 90.3 2 12 6.1 48 4.6 519 37.0 27 12.0 7.5 17 29.7 21 9.1 10 32 20.7 13 7.7 15 8 8.7 15 6.5 2015 10.4 16 4.6

Example 4

Example 4 was prepared and evaluated in the same fashion as Example 1except that the PEG 2000 was replaced with PEG 8000 (polyethyleneglycol8000). The results are shown in Table 6.

TABLE 6 Water 0.9% Saline MBA (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 0.5 71 8.3 116 2.1 1 3 3.0 19 10.3 2 9 25.8 13 5.9 5 5 16.211 8.0 7.5 8 13.3 9 7.8 10 5 9.3 4 5.8 15 8 4.8 7 3.9 20 3 3.5 5 4.5

Example 5

Monomer solutions were prepared and evaluated as described in Example 1except that the amounts of isopropanol and PEG 2000 were varied, keepingthe total amount of isopropanol plus PEG at 55% by weight of thesolution. Coating solutions were then prepared by formulating with S-BPand MBA (5% by weight based on acrylic acid) as described in Example 1.The blue PP (2 layers) was coated, grafted, washed, dried, and evaluatedas described in Example 1. The results are listed in Table 7.

TABLE 7 Water 0.9% Saline PEG (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 5 37 19.0 69 9.8 10 27 15.2 41 8.7 15 14 21.9 18 10.5 20 2816.6 68 9.1

Example 6

Example 5 was repeated except that the coating solutions were formulatedto contain 10% MBA by weight based on acrylic acid. Results forabsorption are shown in Table 8.

TABLE 8 Water 0.9% Saline PEG (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 5 5 9.1 6 7.0 10 8 10.2 8 7.5 15 7 9.6 12 7.1 20 6 9.3 106.7

Example 7

A polymerizable solution was prepared similar to Example 1 using S-BPand comprising 2-hydroxyethylmethacrylate (HEMA, 20% by weight based onthe weight of acrylic acid) and 80% by weight acrylic acid (75%neutralized) with either 5% or 10% MBA (based on the total monomerweight) and various amounts of polyethyleneglycol 6000 (PEG 6000). BluePP (2 layers) were coated, grafted, washed, dried and evaluated asdescribed in Example 1. The results are shown in Table 9 using 5% MBAand Table 10 using 10% MBA.

TABLE 9 Water 0.9% Saline PEG (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 5 50 19.5 107 9.8 10 75 13.2 110 7.8 15 78 14.5 100 8.1 2073 15.7 >120 7.9

TABLE 10 Water 0.9% Saline PEG (%) A_(t) (sec) A_(x) (g/g) A_(t) (sec)A_(x) (g/g) 5 26 8.1 29 6.2 10 20 7.9 18 6.3 15 19 9.3 30 5.9 20 30 7.928 6.6

Foreseeable modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes.

1. An absorbent article comprising: a first substrate; and a copolymerirreversibly bonded onto the first substrate to form a core, wherein thecopolymer is derived from a polymerizable solution comprising: (a) afirst monomer selected from a (meth)acrylic acid or salt thereof; (b)greater than 1 wt % of a second monomer, wherein the second monomer is ahydrophilic crosslinking monomer, and (c) a polymeric porogen wherein atleast 50% of the acidic functional groups in the core are neutralizedwith salt forming cations.
 2. The absorbent article of claim 1, whereinthe polymeric porogen has a molecular weight of at least
 200. 3. Theabsorbent article of claim 1, comprising 1 wt % of the polymericporogen.
 4. The absorbent article of claim 1, comprising the polymericporogen is selected from polyethyleneglycol and polypropyleneglycol andcopolymers thereof.
 5. The absorbent article of claim 1, wherein thepolymerizable solution further comprises a third monomer, wherein thethird monomer is selected from at least one of2-hydroxyethylmethacrylate, 2-hydroxypropyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, N,N-dimethylacrylamide, and acrylamide.6. The absorbent article of claim 1, wherein the second monomer isselected from at least one of methylenebisacrylamide andpolyethyleneglycoldiacrylate.
 7. The absorbent article of claim 1,further comprising a second layer, wherein the second layer is a liquidpervious layer.
 8. The absorbent article of claim 7, wherein the secondlayer is selected from polyester, polyolefin, rayon, cotton, andcombinations thereof.
 9. The absorbent article of claim 7 furthercomprising a third layer, wherein the third layer is a liquid imperviouslayer and the core sandwiched between the second layer and the thirdlayer.
 10. The absorbent article of claim 9, wherein the third layer isselected from a polyolefin.
 11. The absorbent article of claim 1,wherein the first substrate is selected from at least one of athermoplastic and a fabric.
 12. The absorbent article of claim 1,wherein the first substrate is selected from at least one of apolypropylene, polyethylene, polyamide, cotton, and cellulose.
 13. Theabsorbent article of claim 1, wherein the absorbent article is selectedfrom a diaper, a feminine hygiene pad, an animal hygiene pad, a woundcare article, and a chemical absorbent pad.
 14. A method of making anabsorbance article comprising: (a) contacting a polymerizable solutionto a first substrate, wherein the polymerizable solution comprises (i) afirst monomer selected from a (meth)acrylic acid or salt thereof; (ii) apolymeric porogen; and (iii) greater than 1 wt % of a second monomer,wherein the second monomer is a hydrophilic crosslinking monomer; and(b) polymerizing the polymerizable solution to irreversibly bond acopolymer onto the first substrate forming a core, wherein at least 50%of the acidic functional groups in the core are neutralized with saltforming cations.
 15. The method of claim 14, wherein the polymerizablesolution further comprises a Type II photoinitiator.
 16. The method ofclaim 14, wherein the polymerizable solution is contacted to the firstsubstrate by a coating process.
 17. The method of claim 14, wherein thepolymerization is initiated with UV or e-beam radiation.
 18. The methodof claim 14, further comprising washing the core.
 19. The method ofclaim 14, further comprising drying the core.
 20. The method of claim14, where the absorbent article is a roll good.